Solvothermal Synthesis and Luminescence Properties of BaCeF5, and

Publication Date (Web): August 14, 2012. Copyright © 2012 American Chemical Society. *E-mail: [email protected] (Z. Fu); [email protected] (Z. Dai). Telep...
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Solvothermal Synthesis and Luminescence Properties of BaCeF5, and BaCeF5: Tb3+, Sm3+ Nanocrystals: An Approach for White Light Emission Tianqi Sheng,†,‡ Zuoling Fu,*,†,‡ Xiaojie Wang,†,‡ Shihong Zhou,§ Siyuan Zhang,§ and Zhenwen Dai*,†,‡ †

State Key Laboratory of Superhard Materials, College of Physics, and ‡Key Lab of Coherent Light, Atomic and Molecular Spectroscopy, Ministry of Education, Jilin University, Changchun 130012, China § State Key Laboratory of Rare Earth Resources Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China S Supporting Information *

ABSTRACT: Novel monodisperse BaCeF5 and BaCeF5: Tb3+, Sm3+ nanocrystals have been successfully synthesized by a simple one-step solvothermal synthesis. Uniformly distributed nanocrystals with an octahedral morphology and particle size of 75−80 nm were observed. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), photoluminescence (PL), and decay studies were employed to characterize the samples. Under ultraviolet irradiation, the BaCeF5: Tb3+, Sm3+ samples exhibit the typical green emission band of the Tb3+ ions, as well as an orangered and red emission bands of the Sm3+ ions in the presence of Ce3+ ions. The highly intense orange-red and red emission bands of the Sm3+ ions were attributed to the effective energy transfer from the Tb3+ to Sm3+ ions, which has been justified through the luminescence spectra and the fluorescence decay dynamics. The luminescence colors of BaCeF5: Tb3+, Sm3+ nanophosphors can be easily tuned by changing the concentration of Sm3+ ions. These results suggest that BaCeF5: Tb3+, Sm3+ nanocrystals can be explored for three-dimensional displays, back lighting, white light sources, and so on.

1. INTRODUCTION

unstable and the lifetimes of intensities are very low with respect to blue and green phosphors. While most researchers have focused on full-color phosphors, inorganic powder doped with rare earth ions could be considered as an alternative approach due to advantages such as lower production cost, simpler manufacture procedure, free from halo effect, and environmental-friendly characteristics.13−16 Recently, the white light emission was combined with multicolour emission bands of Eu3+, Eu2+, and Dy3+ ions.17 It is also possible to generate the white light emission from these silicate and borosilicate glasses codoped with Tb3+ and Sm3+ ions by UV light excitation.18 In addition, it clearly shows that white light can be obtained in Tb3+/Sm3+ complexes coordinated with Sal/Phen by appropriate combination of blue, green, and red light and have potential applications in solidstate lighting.19 The generation of white light emission largely depends on the energy transfer of excitation energy between rare-earth ions. Furthermore, the energy transfer from a large number of ion pairs has been investigated because of relatively bright room-temperature fluorescence in the visible optical region. However, the energy transfer from Tb3+ to Sm3+ in inorganic powders has been rarely reported.

The preparation of fluorescent nanomaterials have continued to be actively pursued in past decades. The potentially broad applicability and high technological promise of the fluorescent nanomaterials arise from their intrinsically intriguing optical properties, which are expected to pale their bulk counterparts.1−4 Particularly, controllable energy transfer in the nanomaterials has been receiving great interest because it leads luminescence signals to outstanding selectivity and high sensitivity, which are important factors for optoelectronics and optical sensors.5 White light emitting diodes (W-LEDs), the so-called next generation solid-state lighting (SSL) technology, are the current research focus in the lighting industry.6−8 The phosphorconverted (pc) emission method is common for the production for white light emitted LEDs.9 For white light or color displays, simultaneous generation of red, green, and blue (RGB) is necessary. Generally, white light emissions or individual color emissions can be achieved from inorganic compounds by the variation of rare-earth (RE) ion concentration or multilayer approach by changing the excitation wavelength. The presently used red phosphors for blue are near-UV/violet GaN-based LEDs are commercially still limited to divalent Eu ion activated alkaline earth binary sulfides and Y2O2S: Eu3+, respectively.10−12 However, these sulfide-based phosphors are chemically © XXXX American Chemical Society

Received: July 12, 2012 Revised: August 14, 2012

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0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18) samples are synthesized by the same process. 2.2. Characterization. The structural characteristics of the final products were examined by powder X-ray diffraction (XRD) pattern using Cu Kα (λ = 0.15405 nm) radiation on a Rigaku-Dmax 2500 diffractometer. The morphology and the size of the obtained samples were observed with field emissionscanning electron microscopy (FE-SEM, JSM-6700F, JEOL). The ultraviolet−visible photoluminescence excitation and emission spectra were recorded with an Hitachi F-7000 spectrophotometer equipped with a Xe lamp as an excitation source. For measurements of laser-selective spectroscopy, we used the tunable dye laser (bandwidth is less than 0.06 cm−1) pumped by the second harmonic (532 nm) of a pulsed Nd: YAG laser as an excitation source and an Acton SP-2758 spectrograph (resolution 0.023 nm) equipped with a Hamamastsu R-928 photomultiplier tube as the detector. The time-resolved fluorescence decay signals were recorded by a digital oscilloscope and processed with a boxcar integrator. All the measurements were performed at room temperature.

Fluoride nanocrystals doped with rare-earth ions have attracted tremendous interest over past few years because of their unique luminescence properties with useful applications in optical telecommunication, lasers, diagnostics, and biological labels.20−22 The fluoride lattice enables the high-coordination numbers for guest rare-earth ions and the high ionicity of the rare-earth to fluorine bond results in a very wide band gap and low phonon energies. It is very well established that high phonon energies of the host lattices are primarily responsible for nonradiative relaxation in cases of rare-earth ions. The fluoride lattices are superior in comparison to oxygen-based systems as fluorides possess very low vibrational energies and therefore the quenching of the excited states of the rare-earth ions is minimal.23 This leads to a low probability of nonradiative decay for rare-earth ions, and consequently, the luminescence quantum yields are higher than those in the oxides and most other inorganic matrixes.24 Following this, in this work, we realize the solvothermal synthesis of BaCeF5, and BaCeF5: Tb3+, Sm3+ nanocrystals and research luminescence properties of Tb3+ and Sm3+ in octahedral BaCeF5. Moreover, the energy-transfer efficiency from Tb3+ and Sm3+, and the energy-transfer mechanism of Tb3+−Sm3+ in BaCe0.995−yTb0.005SmyF5 nanocrystals have been discussed in detail. Apart from this, we have shown the possibility of changing the color coordinate of the system with an appropriate choice of RE ions concentration. The RE ions content were suitably optimized to get a near white light emission from the sample. The Tb3+ and Sm3+ codoped BaCeF5 system is being reported for the first time.

3. RESULTS AND DISCUSSIONS 3.1. Crystal Structure and Morphologies. Figure 1 presents representative XRD patterns of BaCe1‑xTbxF5 samples

2. EXPERIMENTAL SECTION 2.1. Synthesis of the Samples. 2.1.1. Materials. The samples were synthesized through a solvothermal method. The raw materials BaCO3 (99.0%), Tb(NO3)3·6H2O (99.99%), Sm(NO3)3·6H2O (99.99%), Ce(NO3)3·6H2O (99.99%), and NH4F (99.99%) were all purchased from Sinopharm Chemical Reagent Co. Ltd. and used directly without further purification. 2.1.2. Synthesis. In a typical procedure of preparing BaCeF5 nanocrystals, the first mixture consisted of the following: 2 mmol of Ce(NO3)3·6H2O was first added into 20 mL of isopropyl alcohol with stirring to form a transparent homogeneous solution. Subsequently, the second mixture, consisting of 20 mL of isopropyl alcohol containing 24 mmol of NH4F (0.888 g) and 2 mmol of BaCO3 (0.39468 g), was added into the above solution with stirring to form a transparent homogeneous solution. After the addition of the second mixture into the first mixture, the end mixture became white turbid. After stirring for about 60 min, the resultant solution was transferred into a 60 mL Teflon autoclave. Finally, the autoclave was sealed and heated at 180 °C for 24 h followed by cooling to the room temperature naturally. The resulting precipitates were washed with deionized water and ethanol each two times. The final product was dried at 60 °C for 12 h in air. Then in a typical procedure of preparing BaCeF5: (0.5 mol %) Tb3+, (2.0 mol %) Sm3+ nanocrystals, the first mixture, 1.95 mmol of Ce(NO3)3·6H2O, 0.001 mmol of Tb(NO3)3·6H2O and 0.004 mmol of Sm(NO3)3·6H2O, was first added into 20 mL of isopropyl alcohol with stirring to form a transparent homogeneous solution. The next steps were the same as the preparation of the BaCeF5 nanocrystals. Finally, we can obtain BaCeF5: (0.5 mol %) Tb3+, (2.0 mol %) Sm3+ nanocrystals. Similarly, other BaCe1−x−yTbxSmyF5 (x = 0.005, y = 0, 0.02,

Figure 1. XRD patterns of samples BaCe0.995−yTb0.00 5SmyF5 and reference date JCPDS #43−0394.

with different concentrations. The powder XRD data of the assynthesized product shows nine characteristic diffraction peaks (25.61°, 29.67°, 42.50°, 50.28°, 52.69°, 61.61°, 67.81°, 69.81°) in 2θ range of 20° to 75°. Compared with the cubic structure BaCeF5 (JCPDS # 43−0394, space group Fm-3m [225], cell parameters a = b = c = 6.018 Å), the absence of some diffraction peaks implies that the crystal structure of the assynthesized product may have a higher symmetry in space group. No impurity lines are observed in the patterns of Tb3+ and Sm3+ codoped nanocrystals shown in Figure 1b−k, meaning that the RE3+ doping does not cause significant change in the crystal phases. In addition, it is worth noting that the diffraction peaks are widened as a result of the small-size effect of the nanocrystals. The mean crystallite size of the product was estimated from the XRD pattern according to the Scherrer formula D = Kλ/β cos θ, where λ is the X-ray wavelength (0.15406 nm), β is the full-width at half-maximum, B

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the ⟨100⟩ direction to be faster than those along the ⟨111⟩ direction.26 Therefore, the growth rate of the {100} surface is faster than the {111} surface, and then the fast-growing {100} faces eventually disappeared during growth, resulting in the form of octahedron nanocrystals (Figure S1g). From the above analysis, it can be seen that the nucleation−crystallizationoriented attachment growth process contains obvious evolution stages for the synthesis of octahedral BaCeF5: Tb3+, Sm3+ nanocrystals. The formation process of octahedral BaCeF5: Tb3+, Sm3+ nanocrystals is schematically illustrated in Scheme S1. 3.2. Luminescence Properties. 3.2.1. Photoluminescence Properties of BaCeF5: Tb3+, Sm3+ Nanocrystals. Figure 3a

θ is the diffraction angle, and K is a constant (0.89). The BaCe0.955Tb0.005Sm0.04F5 nanocrystals estimated mean crystallite size is 72.77 nm. Figure 2 shows the FE-SEM image of the sample synthesized at 180 °C for 24 h, illustrating the morphological evolution of

Figure 2. FE-SEM image of the product synthesized at 180 °C for 24 h.

the BaCeF5: Tb3+, Sm3+ octahedral shape. The particle size is about 80 nm, which is in agreement with the calculated crystallite size. For better understanding of the formation process of the octahedral BaCeF5:Tb3+, Sm3+ nanocrystals, reaction products obtained at different growth stages were carefully examined by FE-SEM observations. Figures S1,a−g show the FE-SEM images of BaCeF5 sample synthesized at 180 °C with a reaction time of 0, 2, 8, 12, 16, 20, and 24 h. Before the solvothermal reaction, spherical nanocrystals were formed after the precipitate was stirred for 2 h (Figure S1a). Once the BaCeF5 nuclei were formed, new reactants were continuously arriving at the site. Figure S1b showed the morphology of the products synthesized at 180 °C for 2 h under the solvothermal conditions. We got some accumulated octahedron-like nucleation. When the reaction time was increased to 8 h, the octahedron-like nucleation acted as the centers of crystallization, the crystal growth then followed, and bigger particles grew at the expense of small crystals, which was shown in Figure S1c. As the reaction proceeded, the crystals were further grown on the basis of octahedron-like nanocrystals (Figure S1d). Finally, after 24 h of the reaction, the rapid growth of surfaces planes disappeared, but the slow growth of surfaces planes existed. In general, faces perpendicular to the fast directions of growth have smaller surface areas, and slow growing faces, therefore, dominate the final morphology. So the uniform octahedral BaCeF5: Tb3+, Sm3+ nanocrystals were finally synthesized, as shown in Figure S1g. The size of BaCeF5 nanocrystals increases significantly about from 35 to 80 nm during the whole growth process. It is believed that the reduction in surface energy is the primary driving force for simple particle growth; further reduction in surface energy due to the minimization of high surface energy faces will drive the morphology evolution. From the crystal growth point of view, the shape of the crystal highly depends on the relative growth rates of various crystal planes.25 Generally, the surface energy of the {100} crystal face is higher than that of the {111} face, which causes the growth rate along

Figure 3. (a) Excitation spectrum (λem = 348 nm) and emission spectrum (λex = 265 nm) of BaCeF5. (b) Excitation spectrum (λem = 545 nm) of BaCe0.995Tb0.005F5 and emission spectrum (λex = 265 nm) of BaCeF5.

shows the photoluminescence excitation (λem = 348 nm) and photoluminescence emission (λex = 265 nm) spectra of the BaCeF5 nanocrystals. The excitation spectrum of the BaCeF5 nanocrystals gives a broadband centered at 304 nm with a shoulder centered at 265 nm, which were attributed to the electric dipole-allowed transitions of the Ce3+ ions from the 4f shell to the 5d orbital. Owing to the influences of crystal field splitting and spin−orbit coupling, the 4f→5d transition of the Ce3+ ions will exhibit a subtle structure.27 Under excitation at 265 nm, the emission spectrum of the BaCeF5 nanocrystals exhibits an intense ultraviolet emission band centered at 348 nm, which is assigned to the 5d−4f electronic transition of the Ce3+ ions. Figure 3b shows the photoluminescence excitation (λem = 545 nm) spectrum of BaCe0.995Tb0.005F5 nanocrystals and photoluminescence emission (λex = 265 nm) spectrum of the BaCeF5 nanocrystals. The photoluminescence excitation (λem = 545 nm) spectrum of BaCe0.995Tb0.005F5 nanocrystals in Figure 3b is similar to the photoluminescence excitation (λem = 348 nm) spectrum of the BaCeF5 nanocrystals in Figure 3a. On the basis of the above photoluminescence excitation spectrum of Tb3+-doped samples and photoluminescence spectrum of no Tb3+-doped samples, we can find that the emission band of Ce3+ overlaps well with the excitation band of Tb3+.28,29 Therefore, it is expected that a resonance-type energy transfer from Ce3+ to Tb3+ in Tb3+-doped BaCeF5 nanocrystals may occur.30 Figure 4 gives the photoluminescence excitation (λem = 597 nm) and photoluminescence emission (λex = 304 nm) spectra of the BaCe0.955Tb0.005Sm0.04F5 nanocrystals. When the 597 nm emission of Sm3+ was monitored, the BaCe0.955Tb0.005Sm0.04F5 nanocrystal shows a broad excitation band peaking at 304 nm. C

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because La3+ ions have no radioluminescence. Figure 6 displays the emission spectra of the BaCe0.955F5: (0.5 mol %) Tb3+, (4.0

Figure 4. Excitation (λem = 597 nm, left) and emission (λex = 304 nm, right) spectra of BaCe0.955Tb0.005Sm0.04F5. Figure 6. Emission spectra of BaCe 0.955 Tb 0.005 Sm 0.04 F 5 and BaCe0.955Tb0.005La0.04F5 (λex = 265 nm).

With 304 nm excitation, the photoluminescence emission spectrum of BaCe0.955Tb0.005Sm0.04F5 has characteristic transitions of forbidden f−f transitions within the Sm 3+ configuration in the wavelength range of 567−640 nm. The characteristic emissions of Sm3+ at 567 nm, 558 nm (green), 597 nm (orange-red), and 640 nm (red) can be attributed to the transitions 4G5/2→6H5/2, 4G7/2→6H5/2, 4G5/2→6H7/2, and 4 G5/2→6H9/2, respectively. 3.2.2. Energy Transfer and Luminescence Mechanism in BaCeF5: Tb3+, Sm3+ Nanocrystals. To explore the possibility of the energy transfer from the Tb3+ to Sm3+ ions, Tb3+ ions with the same concentrations (0.5 mol %) and Sm3+ ions with different concentrations were doped into the BaCeF5 nanocrystals. Figure 5 displays the emission spectra of the

mol %) Sm3+ nanocrystals and the BaCe0.955F5: (0.5 mol %) Tb3+, (4.0 mol %) La3+ nanocrystals. Compared with the emission spectrum of BaCe0.955F5: (0.5 mol %) Tb3+, (4.0 mol %) Sm3+, correspondingly, the characteristic emission intensities of Sm3+ at 558, 567, and 597 nm increase obviously. The results suggested that an obvious energy transfer from Tb3+ to Sm3+ in BaCeF5: Tb3+, Sm3+ nanocrystals may occur. To investigate the energy-transfer process from Tb3+ to Sm3+, their decay curves were also recorded. Figure 7 shows the luminescence decay curves of Tb3+ and Sm3+ for 545 and 597 nm emissions in the case of the BaCe0.995−yTb0.005SmyF5 (y = 0.04, 0.06, 0.08, 0.16) samples. In each case, the fluorescence lifetime (τ) for transition 4G5/2→6H7/2 of Sm3+ is ∼3.17 μs which increase to ∼3.23 μs and lifetime (τ) for transition 5 D4→7F5 of Tb3+ is ∼574.03 ms which lowered to ∼63.37 ms for BaCe0.995−yTb0.005SmyF5 (y = 0.04, 0.06, 0.08, 0.16) samples. It can be seen that on increasing Sm3+ concentration in all codoped samples the lifetimes of green (545 nm) emission bands of Tb3+ ions decrease while the lifetimes of orange-red (597 nm) emission bands of Sm3+ increase. We interpret this decrease of lifetime as evidence for a nonradiative (probably resonant) transfer to the Sm3+ ion, which also confirmed efficient energy transfer. Therefore, the result demonstrates that the energy-transfer process occurs between Tb 3+ and Sm3+.31−33 Accordingly, the energy transfer efficiency from Tb3+ to Sm3+ can be calculated according to the following expression, τ ηT = 1 − s τs0

Figure 5. Emission spectra of BaCe0.995−yTb0.005SmyF5 (λex = 265 nm).

BaCe0.995−y Tb0.005SmyF 5 nanocrystals with different Sm3+ concentrations; it contains both the strong green emission of the Tb3+ ions and weak orange-red emission of the Sm3+ ions. The emission intensity of the Sm3+ ions gradually increases at the expense of that of the Tb3+ ions with the increase of Sm3+ doping concentration, indicating that the energy transfer from the Tb3+ to Sm3+ ions is highly efficient since the emission band of the Tb3+ ions matches well with the f−f absorptions of the Sm3+ ions. Until BaCe0.955Tb0.005Sm0.04F5 the emission intensity of Sm3+ ions is the strongest, and then the emission intensity of Sm3+ ions gradually decreases with the increase of Sm3+ doping concentration. To confirm the energy transfer from the Tb3+ to Sm3+ ions, BaCe0.955F5: (0.5 mol %) Tb3+, (4.0 mol %) La3+ nanocrystal was prepared by the same solovthermal method

where τs0 is the lifetime of the sensitizer in the absence of the activator and τs is the lifetime of the sensitizer in the presence of the activator. In our case, Tb3+ and Sm3+ ions play the roles of the sensitizer and activator, respectively.34,35 The ηT is calculated as a function of the content of Tb3+−Sm3+ pair (n), which is represented in Figure 8. The ηT was found to increase with an enhancement in the Tb3+−Sm3+ content and reach to about 74% when n is 0.18. The high-energy efficiency indicates that the energy transfer from the Tb3+ to Sm3+ ions is the dominant reason for the increase in the Sm3+ emission intensity, instead of the energy absorption by the Sm3+ ions themselves, which can be also supported by the optical D

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Figure 7. Decay curves of Tb3+ (545 nm) and Sm3+ (597 nm) emission transitions in BaCe0.995−yTb0.005SmyF5 samples (y = 0.04, 0.06, 0.08, 0.16).

resulting in green and yellow emissions (495, 545, and 584 nm). Tb3+→Sm3+ energy transfer may be depicted by ET from 5 D4 level of Tb3+ to 4G9/2 level of Sm3+, and then the Sm3+ ions at 4G9/2 level decay nonradiatively (NR) to the lower levels (4G7/2, 4G5/2). Finally, Sm3+ ions at the 4G7/2 level and at the 4 G5/2 level decay radiatively to the ground state (6H5/2), resulting in green emissions (567, 558 nm). At the same time, Sm3+ ions at the 4G5/2 level decay radiatively to the 6H7/2 level, resulting in orange-red emission (597 nm). 3.2.3. White Light Emission in BaCe0.995−yTb0.005SmyF5 Samples. An effective approach for white light emission in the BaCe0.995−yTb0.005SmyF5 as the sensitizing agent under UV radiation is demonstrated and the luminescence colors (green, orange-red, red) of the Tb3+, Sm3+ codoped BaCeF5 samples are shown in the inset of Figure 5. The color coordinates are characterized by the CIE chromaticity diagram and are shown in Figure 10. The chromaticity parameters of the polymer material are tabulated in Table 1 for different concentrations of Sm3+ ions which can be effectively tuned to white light with coordinates (0.31, 0.34) by changing the activator concen-

Figure 8. Energy-transfer efficiency ηT in BaCe0.995−yTb0.005SmyF5 (y = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18).

properties of the BaCe0.995−yTb0.005SmyF5 samples (y = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18). To further recognize the down-conversion mechanisms in the sample, possible down-conversion processes are schematically given in the energy level diagrams of Ce3+, Tb3+, and Sm3+ as shown in Figure 9. In the case of the energy transfer (ET) of Ce3+−Tb3+, excited 5d state of Ce3+ can transfer energy to 5D4 level of Tb3+ ions and Tb3+ ions at the 5D4 level decay radiatively to the ground state (7F6), 7F5 level and 7F4 level

Figure 9. Schematic energy-level diagram explaining the luminescence process and the possible energy-transfer pathways for the BaCe0.995−yTb0.005SmyF5 (ET: energy transfer, NR: nonradiative).

Figure 10. CIE color coordinate diagram of the BaCe0.995−yTb0.005SmyF5 samples. E

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by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.

Table 1. Table Showing the Color Coordinates Using Commission International de Enclairge (CIE) for BaCe0.995−yTb0.005SmyF5 sample

CIE(X)

CIE(Y)

BaCe0.995Tb0.005Sm0F5 BaCe0.975Tb0.005Sm0.02F5 BaCe0.955Tb0.005Sm0.04F5 BaCe0.935Tb0.005Sm0.06F5 BaCe0.915Tb0.005Sm0.08F5 BaCe0.895Tb0.005Sm0.10F5 BaCe0.875Tb0.005Sm0.12F5 BaCe0.855Tb0.005Sm0.14F5 BaCe0.835Tb0.005Sm0.16F5 BaCe0.815Tb0.005Sm0.18F5

0.37 0.33 0.34 0.34 0.33 0.31 0.31 0.30 0.29 0.28

0.17 0.44 0.41 0.39 0.37 0.35 0.34 0.32 0.32 0.30

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tration. The luminescence colors of the sample BaCe0.875Tb0.005Sm0.12F5 is nearly to white light. This is very important for lighting applications because the desired emission characteristics match well with the standard white (0.33, 0.33) of the CIE chromaticity diagram. It clearly shows that white light can be obtained in Tb3+ , Sm 3+ codoped BaCeF 5 nanocrystals by appropriate combination of green, orange-red, and red light and have potential applications in solid-state lighting.

4. CONCLUSION To summarize, a simple solvothermal method has been used to prepare BaCeF5 and BaCeF5: Tb3+, Sm3+ nanocrystals. The XRD and FE-SEM analysis indicated that the samples crystallized in cubic structure with octahedral morphology and an average diameter of 80 nm. The photoluminescence spectra of BaCe1−x−yTbxSmyF5 nanocrystals demonstrated that the energy transfer from Ce3+ to Tb3+ and Tb3+ to Sm3+ may occur in the same time. The photoluminescence spectra of BaCe0.995−yTb0.005SmyF5 nanocrystals show this result, the emission intensity of the Sm3+ ions is the strongest when the concentration of Sm3+ is 4.0 mol %. The luminescence colors of the sample BaCe0.875Tb0.005Sm0.12F5 is nearly to white light. Such efficient white light emission of the Tb3+/Sm3+ codoped BaCeF5 nanocrystals makes them excellent candidates applicable in solid-state lighting.

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ASSOCIATED CONTENT

* Supporting Information S

The whole growth process description of the material. This material is available free of charge via the Internet at http:// pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (Z. Fu); [email protected] (Z. Dai). Telephone: 86-431-85167966. Fax: 86-431-85167966. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Science Foundation of China (no. 11004081), partially supported by the Science and Technology Innovation Projects of Jilin Province for overseas students and sponsored by Project 450091202144 Supported by Graduate Innovation Fund of Jilin University and F

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